Boosted by retail hiring for the holiday season, San Diego County’s unemployment rate in December fell to its lowest level since 2008.

The 8.1 percent mark announced Friday continues a trend of incremental drops in the region’s jobless rate since a peak of 10.9 percent in July 2010.

In the past year, the county reported a net gain of 20,300 positions. Job creation during that time was strongest in sectors such as retail trade, tourism and administrative services. Manufacturing was the only industry to post a year-over-year decline.

“We’ve lost a lot of the good middle-income types of jobs. As a result of that, people don’t have as much money to spend,” said Alan Gin, an economist at the University of San Diego.

The rate for last month compares with 9 percent from the same period a year earlier and 7.4 percent in December 2008, the last time the rate was below 8 percent. (The national jobless rate for last month was 7.8 percent.)

Employers in San Diego County added a net 700 jobs last month, with the retail trade industry providing the biggest boost during the holiday season. Retail salespeople earn an average of $13 per hour, according to state data.

The 700 figure was a big decline from November, which had a revised net gain of 8,300 positions. Retail also led the hiring spur that month.

“We actually went back to the norm in December,” Gin said. “Retailers and others were anticipating a really strong Christmas season, so they did a lot of hiring in November.”

Overall, holiday retail sales came in below what the National Retail Federation had projected. They totaled $579.8 billion, up 3 percent from the previous year, but the federation had estimated a 4.1 percent jump.

Economists have said the less-than-expected results could have resulted from consumer anxiety over the tax and spending showdown in Congress during the final days of 2012. Another theory is that people finished their holiday shopping sooner than usual because there were more shopping days between Thanksgiving and Christmas.

“Although last month’s job numbers could well be revised higher, the slowdown in hiring may have reflected the uncertainty about the ‘fiscal cliff,’ which has hampered the hiring and investing of many firms,” said Lynn Reaser, chief economist at Point Loma Nazarene University.

Just after New Year’s, President Barack Obama and Congress finalized legislation dealing with taxes. But they postponed resolution of two other crucial parts of the “fiscal cliff” standoff — raising the nation’s debt ceiling and addressing a raft of major spending cuts called sequestration — for at least two more months.

Defense cuts that are part of sequestration would have a big impact on San Diego County, which is home to a large defense industry. The San Diego Regional Economic Development Corporation estimates that 30,000 defense-related jobs could be at stake.

Uncertainty on these issues will likely continue to keep hiring slow for local defense firms, said Kelly Cunningham, an economist at the National University System Institute for Policy Research.

“I’m sure the defense contractors are sitting back,” he said. “They’re waiting for a little more clarity, and it just gets kicked down the road.”

Reaser said the overall economic outlook for San Diego County is positive. She projects that 25,000 jobs will be added in the region this year.

“The job performance for all of 2012 clearly shows that San Diego’s economy is on the mend,” Reaser said.

Cunningham estimates regional job growth of 21,000 positions in 2013.

Statewide, the jobless rate remained at 9.8 percent last month — the same rate as in November, the state Employment Development Department said Friday. The figure held steady after dropping below 10 percent in November for the first time since the start of the recession.

The department said 1.8 million Californians were unemployed in December, slightly below the previous month but down by 255,000 since December of 2011. The unemployment rate at the time was 11.2 percent.

The department also said the fields of educational and health services, construction and information services reported the biggest job gains between November and December.

Still, the agency’s surveys showed that nonfarm payroll jobs decreased by 17,500 during December, demonstrating the continued volatility in the labor market, said economist Steven Levy of the Center for the Continuing Study of the California Economy.

He said the state has made important gains since a year ago as its economy continues to rebound.

“Looking at the past 12 months, California has slightly outpaced the nation in job growth, which is expected to continue in 2013,” he said. “While the state benefits from a surge in technology jobs, a rebound in tourism and rising construction levels, California’s growth is still tied to the uncertainties in the national economy around fiscal challenges and the slower world economy growth.”

Mining and logging, manufacturing, government and other services have continued to see falling job numbers during the past year, losing more than 51,000 jobs, according to the state jobs report.

Government lost the highest number of jobs — about 31,500 in the past year.